Speaker
Description
The longitudinal structure of the quark–gluon plasma (QGP) is the missing third dimension in our picture of its initial state. It records how energy is deposited along the beam, how quantum fluctuations in the colliding nuclei shape the plasma, and how collective expansion converts this geometry into final-state momentum correlations. Accessing it is notoriously difficult: short-range nonflow correlations from jets and resonance decays obscure the long-range flow signal, while conventional factorization ratios provide only an indirect view. We introduce a strategy that turns nuclear shape into a controlled instrument. Subtracting correlations from similarly sized nuclei with different deformations cancels the common nonflow and fluctuation-driven baseline, isolating the deformation-driven signal. In transport simulations, deformation strongly changes the elliptic-flow amplitude while nearly preserving its normalized longitudinal profile, allowing this signal to recover the full two-rapidity correlation map. The map reveals a nonlinear, nonadditive loss of correlation and a previously unquantified, acceptance-dependent bias in standard flow measurements. Existing U+U/Au+Au, Ru+Ru/Zr+Zr, and O+O/Ne+Ne data can test the method immediately and extend it to longitudinal fluctuations in ellipticity, triangularity, and transverse size. Known nuclear shape thereby becomes a precision instrument for three-dimensional QGP imaging.
